1. Technical Field
The present invention in its most general aspect refers to the sector of electronics, and more in particular to a circuit architecture of organic nature, also called an organic base, and a related manufacturing method.
2. Description of the Related Art
As is known, circuit architecture in electronic devices are generally obtained through photolithographic methods.
In particular, photolithographic technique or photolithography is a process of a photographic nature which is employed to trace microgeometries on a silicon wafer, and in microelectronics it is used to transfer the design of a photomask on such wafer.
Photolithography essentially comprises three main operations which, even if known, are briefly described below so to better elucidate the present invention.
A first operation consists of drawing the geometric configuration (design), to be transferred later on a microscopic scale, on a sheet in a much greater scale than the final microscopic scale, so that the start design can be carried out with conventional methods and specifications.
The design is then photographed and reduced to the microscopic scale of actual interest, on a glass sheet or other materials, the so-called photomask.
The second operation consists of transferring the design of the photomask on the surface layer of the silicon wafer (substrate), on which a photo-sensitive emulsion layer is first applied, generally a polymer, called a photoresist.
In such operation, the transfer of the design is obtained by projecting the design of the photomask with an ultraviolet light beam onto the photoresist layer and then developing with a chemical etching, according to the normal photographic method.
Then, either the portions of the photoresist unaffected by light, which are therefore soluble in the developer bath (negative lithography), are removed or the photoresist portions are exposed and hence rendered soluble in the developer bath (positive lithography) are removed.
Therefore, the design geometry will be reproduced on the wafer which was initially drawn on the photomask due to the photo-incision made on the photoresist through the ultraviolet radiation.
The third operation consists of subjecting the substrate thus treated to a chemical-physical process such as, for example, diffusion of doping material, vacuum deposition of new material, or ion implantation, through which, at portions no longer covered by the photoresist, the substrate is modified so to create predetermined desired characteristics for the electronic conduction.
Then, the residue portions of the photoresist are also chemically removed.
The aforesaid operations are repeated as many times on the same wafer, with different photomasks employed, as needed to realize complex structures which then give rise to electronic devices.
Regarding the aforesaid photoresist, it should be noted that they are generally polymers with molecular weights normally in the range of 100,000-200,000 dalton whose properties, including viscosity, softening temperature, and degradation temperature, are optimized according to the specific case by acting in fact on the molecular weight.
A conventional photoresist mixture is typically composed of: a resin base, or binder which ensures mechanical properties of the mixture (adhesion, chemical strength etc.); a solvent which controls a number of the mechanical properties (for example the viscosity of the mixture); and a photo-active material (photo-active compound (PAC)), which specifically is the photoresist which in turn can be of negative or positive type, as will be clearer below.
A negative photoresist is used in negative photolithography processes, in which after exposure to UV radiation, a chemical etching treatment (chemical attack) eliminates the photoresist portion not exposed to the light.
In this case, the photoresist mixture, containing the precursor monomers or oligomers for exposure to the incident UV radiation, undergoes a photo-polymerization and/or photo-cross-linking reaction.
The cross-linking of the photoresist determines an increase of its molecular weight, which induces a diminution of the solubility of the photoresist in some solvents.
Examples of negative photoresists are reported below, and comprise:                Mixtures of alkenes and azides or bisazides.        
The azides are photo-decomposed by UV action into highly reactive species of a radical nature, such as nitrenes.
The latter, reacting with the unsaturated reactive sites of the alkenes, lead to the formation of the respective polymers, through three different possible types of non-selective reaction, corresponding to double bond cycloaddition, insertion reaction of C—H bonds, and elimination reaction of hydrogen atoms.
Poly(p-hydrostyrene) with monofunctional bisazides or azides represent a typical photoresist mixture.                Polyamides.        
In this case, the acid groups of the precursor of the polyimide, poly(amic-acid) are functionalized with methacrylated groups and deposited in the presence of appropriate non-radical photo-active initiators.
The exposed photoresist portions then undergo cross-linking reactions, while, through the treatment with an appropriate solvent, the non-exposed portions are removed.
The resulting image is then subjected to a heat treatment (annealing), so to degrade the methacrylated units.
By means of cyclization of the poly(amic acid), the most stable polyamide is formed.                Polymers which have side-chain maleimide groups capable of giving photodimerization reactions.        Copolymers of tetrathiafulvalene (TTF) and poly(chloromethylstyrene) (PSTFF).        
In the presence of electron-acceptor species (for example halides) and after exposure to radiation X, the comonomers polymerize by charge transfer reactions.
A positive photoresist is instead used in a positive lithography process in which, after exposure to UV radiation (deep UV, extreme UV or electron beam radiation [e-beam photolithography]), an etching treatment eliminates the photoresist portion exposed to the light.
In this case, the mixture of the photoresist containing the polymer undergoes a photo-degradation reaction due to the exposure to the incident UV light.
In such degradation reaction, several of the covalent bonds of the polymer chain are broken and the molecular weight of the polymer decreases.
The monomer or oligomer fragments, being more volatile and/or soluble in the etching solvents, are subsequently eliminated.
Known examples of positive photoresists are reported below, and comprise:                Acrylated, methacrylated polymers, their respective fluorinated and oximine derivatives, and their copolymers, including polymethylmethacrylate (PMMA).        
A widely used polymer in e-beam photolithography, since it is provided with excellent properties of adaptation to the underlying layer (coating) and of development, is the poly (2,2,2-trifluoroethylmethacrylate).                DQN, where DQ represents the photo-active diazoquinone and N represents the compound known with the name of Novolac, a phenol resin.        
After exposure to UV radiation, the photo-active bond C—N2 of DQ, which renders the polymer insoluble in the deposition mixture, is broken, with the liberation of N2 and formation of a carboxylic group which makes the photoresist soluble.                Polybutenesulfone (PBS) and alkene-sulfone copolymers such as, for example, PBS with 5-hexen-2-one, which has shown optimal coating, adhesion and image properties in this polymer class.        
After exposure to UV radiation, the polymer skeleton is broken and the fragments obtained convert into sulphur dioxide (SO2) and alkenes.                Positive photoresists can also be composed of mixtures which, after exposure to UV radiation, undergo photo-catalyzed degradation reactions.        
In these cases, a sensitizer is added to the mixture, i.e., an additive containing photo-labile groups, often photo-induced acid-generators, which catalyze the degradation of the polymer and the consequent diminution of its molecular weight.
An example of this type of photoresist are mixtures of poly(acetaldehyde) or poly(formaldehyde) with poly(vinyl chloride) and small quantities of electron-attractors.
From that set forth above, it is clear that in the conventional photolithography processes as described, a photoresist constitutes a sacrificial material, in the sense that, in such processes, a photoresist layer is deposited so as to be removed later, its use being directed towards the transfer of a geometric configuration (design) from a photomask to a layer of a different material, on which it is deposited.
In particular, it should be noted that, in a circuit structure obtained by means of photolithography as described above, the photoresist employed is entirely removed during the process and therefore the final circuit structure will not comprise any photoresist layer.
The photoresist is in fact entirely removed through two distinct steps, a first etching step being carried out after exposure to UV radiation in order to transfer the desired design onto the wafer, a second etching step carried out after the wafer has been subjected to one of the aforesaid processes of chemical-physical nature, in order to confer predetermined electronic conduction characteristics to the substrate portions not covered by the photoresist.
Therefore, even if in keeping with the object, it should be noted that, overall, the known processes for manufacturing circuit architectures through the use of photolithography and photoresists as described above are not free of drawbacks, including the main drawback of having to carry out a high number of steps as a consequence of the use of photoresist layers as sacrificial material.
It should moreover be considered that, in the sector of hybrid electronics, that is, in case of circuit structures or architectures on an organic base, further steps of manufacturing and/or integration of the organic components in the particular circuit architecture are to be carried out.